Had he believed Zira meant his protests, he would have relented, giving the Angel his (first round of) pleasure without any more torment. However, he saw the subtle way his cock twitched at the thought, enough to have him reaching up to brace himself against the headboard, presenting his obviously-larger cock to Zira's mouth.
"Suck me, beloved, and then perhaps I'll let you come," He knew Aziraphale enjoyed Crowley's power trips on occasion, and more importantly, he was in one of his Moods, which the Angel was usually kind enough to just humor. Besides, with how hard he was already, it wouldn't take Zira long to earn his 'reward'.